The vials of smallpox discovered in the NIH research lab were completely sealed, so it's extremely unlikely anyone was exposed to the virus, McFadden said. In addition, now that the vials are in the hands of the CDC, they're in one of the two laboratories in the world with the necessary safety protocols and approval to handle the virus. (The other known place that houses live smallpox is a laboratory in Koltsovo, Russia.)
Even if someone were infected in a lab accident, there's an almost nonexistent risk of the disease spreading in the general population, Adalja said.
People aren't infectious until they start showing the characteristic rash. So health workers have time to implement a "ring strategy" of containment, meaning any exposed person would be quarantined and vaccinated, and all the people they come into contact with would be immunized against the disease. The same ring strategy successfully eliminated the disease in the 1970s, Adalja said.
The risks from a lab accident are extremely low, but there's still a murky, impossible-to-quantify risk that rogue nations or terrorists could try to deploy smallpox as a weapon, McFadden said. The Russians did try to make biological weapons from viruses, such as Ebola, during the Cold War.
"Nobody knows if there are weaponized stockpiles of Variola virus out there or not," McFadden told Live Science.
If someone were to deploy a weaponized form of the virus, few people today would have any immunity, meaning it could theoretically be more infectious than it was in the past, Adalja said.
But on the other hand, because of the bioterrorism threat, the United States has protocols in place to quickly contain a smallpox outbreak, and has stockpiles of the smallpox vaccine, he said.
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